Optical absorption and photoluminescence (PL)
measurements were performed on single crystals of undoped Y3Al5O12 (YAG) and a
number of rare-earth-doped YAG to study the effect of dopant type and
concentration, growth atmosphere, post-growth annealing and UV irradiation on
the optical properties of YAG crystals. The presence of hydrogen in the growth
atmosphere was found to be essential for enhancing the incorporation of Ce ions
in the Ce3+ state in Ce-doped YAG (Ce : YAG). Annealing in air was shown to
have no effect on the PL emission of Ce : YAG crystals. An absorption peak
around 256 nm was observed in the undoped YAG and Ce : YAG crystals after air
anneal at 1200 °C. Optical absorption and annealing experiments support the
association of the 256 nm peak with Fe impurities and oxygen ions. UV
irradiation modifies the valency of impurities and generates electronic defects
leading to an increase in the optical density of YAG crystals. Optimizing the
growth and annealing conditions is critical in order to develop Ce : YAG single
crystals as efficient scintillators.
Source:IOPscience
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